The invention relates to a spring washer for the securing of screws, nuts or the like with an essentially ring-shaped washer body of a certain thickness having a washer top side and a washer under side, wherein the washer under side is subdivided into an outer ring surface and an inner ring surface and the washer in an unstressed state rests with the outer edge of the outer ring surface on a flat base and the outer ring surface and the inner ring surface form an acute angle with this flat base.
Spring washers have the function to counteract loosening processes in screw connections. Loosening processes of this type result from initial stressing force losses in the screw connections which arise as a consequence of settling and/or creeping processes in the parts which are screwed together.
In order to avoid loosening processes, the spring washers must have a sufficient spring tension over a certain travel of the spring which can compensate an initial stressing force loss generated by the settling or creeping processes to the extent that the required clamping force for the operating reliability of the screw connection is maintained.
Various washer constructions have already been proposed for the attainment of a sufficient spring tension over a certain travel of the spring. The simplest washer construction of this type is represented by the tightening disk according to DIN 6796. In this known construction, the outer ring surface merges with equal thickness of the washer body directly into the inner ring surface without recognizable subdivision. For example, DE-AS 20 61 297 discloses a further construction of this type. In this construction the washer under side is subdivided by a step into the outer ring surface and the inner ring surface. Therefore, by tightening of the screw connection the outer ring surface is first pressed onto the base, whereby an initial spring tension with a certain spring travel results. Then by further tightening, the initiation of force follows over the relatively steep step, whereby a relatively high spring tension results for a very small spring excursion. However, by virtue of the lever effect of the step the danger exists that by a further tightening process the outer edge of the outer ring surface lifts up from the base such that finally the entire load lies only in the region of the step. Therefore, this region is also burdened the most. Thus, washer constructions of this type are only suitable for such securing tasks which may be exposed to high specific surface pressures in the region of the support under the step.
DE-OS 40 25 146 discloses a further washer construction. In this known construction, the outer ring surface uniformly merges, i.e. without a step or the like, into the inner ring surface. However, the transition region in this washer construction has a smaller cross-section than the remaining region of the washer body. This smaller cross-section in the transition region is achieved by a circular groove arranged on the washer top side. By virtue of this circular groove on the washer top side, washer constructions of this type have the tendency to "gape", i.e. the tendency to lift up in the region of the outer edge of the outer ring surface, especially at low thickness of the washer body and too great a starting torque.
The so-called "gaping" in washer constructions of this type can be reduced in its effect by forming the part of the washer body having the outer ring surface as a relatively large area. This means that washer constructions of this type produce their full securing effect, especially with a large outer diameter.